Smart cards are becoming increasingly more popular for security and personal identification applications. For example, smart cards are currently used for storing sensitive data such as medical records, banking information, etc. In perhaps their most common form, smart cards have a card body which resembles a credit card in size, shape, and thickness, and they may even be made out of similar materials, such as plastic. Yet, rather than simply having a magnetic stripe to store sensitive information (e.g., account numbers, user identification, etc.) as standard credit cards do, smart cards generally include an integrated circuit (IC). The IC not only includes a non-volatile memory for storing such sensitive information, but it may also include a microprocessor for processing this information and communicating with a host device via a card reader, for example. Accordingly, not only can smart cards store more information than magnetic stripe cards, but they also have much greater functionality.
Various protocols have emerged to standardize the operation and communications of devices such as smart cards. One of the earliest of these was developed by the International Organization for Standardization (ISO) and is known as the ISO 7816-X protocol. In particular, this protocol is set forth in ISO documents ISO 7816-1 (Physical Characteristics), ISO 7816-2 (Dimensions and Locations of Contacts), ISO 7816-3 (Electronic Signals and Transmission Protocols), ISO 7816-10 (Electronic Signals and Answer to Reset for Synchronous Cards), and ISO 7816-12 (USB Interface), for example, all of which are hereby incorporated herein in their entirety by reference.
Furthermore, in response to the increasing popularity of the universal serial bus (USB) architecture, increasing numbers of smart cards continue to be developed which operate in accordance with the USB protocol. This protocol is set forth in the Universal Serial Bus Specification, Revision 2.0, Apr. 27, 2000, published by USB Implementers Forum, Inc., which is hereby incorporated herein in its entirety by reference. The USB architecture is particularly advantageous in that it provides a standard “plug and play” interface for devices external to a computer, for example. That is, external peripheral devices can be relatively quickly and easily installed and removed from a host device, such as a computer, without having to open or power down the computer.
In accordance with the USB Specification, the host device operates as the master of the system bus, and all of the USB devices connected to the system bus operate as slave devices. A USB system bus includes two data lines D+ and D−, over which differential serial data signals are transmitted. Moreover, the USB system bus also includes a power line VBUS which may be used to provide an operating voltage from the host device to USB devices without their own source of power, as well as a ground line.
Accordingly, upon connection to the system bus, a USB smart card will receive power from the power line VBUS which will cause its processor to initialize and announce its presence so that the host device will recognize the device. This is done by connecting a predetermined voltage (e.g., 3.3 V) as an attachment signal to one or both of the data lines D+, D− via a respective pull-up resistor depending upon the data transfer speed at which the smart card is to operate. In particular, the USB Specification defines three data transfer rates, namely low speed (1.5 Mb/s), full speed (12 Mb/s), and high speed (480 Mb/s).
Generally speaking, once the USB smart card is recognized by the host device, the smart card will send information identifying itself and its capabilities to the host device when prompted. This information is incorporated within various descriptors, namely device descriptors, configuration descriptors, interface descriptors, endpoint descriptors, and (optionally) string descriptors. Further information on USB descriptors may be found in the USB Specification. The host device will interpret this data using an appropriate driver and then inform the smart card what configurations and system resources it will be allotted during the current session. The smart card uses this information to enumerate itself for use in the system.
One particularly advantageous approach for managing pull-up connections to the differential data lines is disclosed in U.S. Application Ser. No. 2002/0066791 to Leydier et al., assigned to the assignee of the present application, and which is hereby incorporated herein in its entirety by reference. In particular, this application is directed to a smart card which has an IC with voltage conditioning circuitry and a pull-up resistor. The smart card, when inserted in a smart card adapter coupled to a host device, is capable of signaling the host device over a bus using the integrated pull-up resistor selectively coupled to a voltage output of the voltage conditioning circuitry and a first output of the smart card.
The voltage conditioning circuitry output is selectively coupled to the first output through the resistor responsive to the device being powered by the bus (but not transmitting). This tends to pull up the first output to the voltage level of the voltage source, which makes the smart card capable of being properly detected by the host device upon the bus being driven by a host. Selectively disconnecting the pull-up resistor while the smart card is transmitting or receiving results in a more balanced differential output signal. Since the pull-up resistor and voltage conditioning circuitry supplying the proper voltage to the pull-up resistor are an integrated part of the IC, no separate contact is required to supply voltage to the resistor. This permits the smart card to be compatible with the contact configuration of certain existing smart cards, and eliminates the need for the pull-up resistor or voltage conditioning circuitry to be included in the smart card adapter.
Moreover, the device may also be detached from the system bus for other reasons. For example, the device may be detached to perform a re-enumeration, to conserve power, to reduce communications overhead processing by the host device, or when the VBUS power supply is not within the range specified by the USB Specification.
Because of the enhanced functionality afforded by the USB Specification and the significant computing power which may be included in USB smart card integrated circuits, it is possible not only to support multiple applications with a smart card, but also multiple configurations, such as endpoint configurations, for example. An example of a USB device which supports two different endpoint configurations is disclosed in U.S. Pat. No. 6,122,676 to Brief et al. In particular, this patent is directed to a USB device which includes two mappings for relating a received token to an endpoint pipe. A host controller selects which of the two mappings the USB device will use during initialization or enumeration, and the host controller can also cause the USB device to change between the two configurations during operation.
While the above USB smart card devices provide improved operational flexibility, greater flexibility may be required in certain applications to achieve desired bandwidth utilization or even security against attacks to the USB system, for example.